An actuator unit is used in a railway vehicle, for example, with being interposed between a vehicle body and a truck in order to suppress vibration in a left-right direction relative to an advancing direction of the vehicle body.
JP2010-65797A discloses an actuator unit including: a cylinder; a piston slidably inserted into the cylinder; a rod inserted into the cylinder and coupled to the piston; a rod side chamber and a piston side chamber defined within the cylinder by the piston; a tank; a first opening/closing valve provided on midway of a first passage that communicates the rod side chamber with the piston side chamber; a second opening/closing valve provided on midway of a second passage that communicates the piston side chamber with the tank; a pump that supplies a working fluid to the rod side chamber; a motor that drives the pump; a discharge passage that communicates the rod side chamber with the tank; and a variable relief valve provided on midway of the discharge passage.
According to this actuator unit, a direction of an output thrust is determined by appropriately opening and closing the first opening/closing valve and the second opening/closing valve, whereupon the pump is rotated by the motor at a fixed speed such that the fluid is supplied into the cylinder at a fixed flow rate. Meanwhile, an internal pressure of the cylinder is controlled by adjusting a relief pressure of the variable relief valve, and in so doing, a thrust of a desired magnitude can be output in a desired direction.